Isotope separating apparatus



Sept. 16, 1958 Filed Oct. 11. 1945 United States Patent ISOTOPE SEPARA'HNG APPARATUS 7 Michael K. Kudravetz and Harold B. Greene, Oak Ridge, Tenn., assignors, by mesne assignments, to the United States of America as represented by the United States Atomic Energy Commission Application October 11, 1945, Serial No. 621,846 7 Claims. (Cl. 250-413) The present invention relates to apparatus for separating charged particles, such as ions, by utilizing the magnetic mass spectrum thereof and particularly to a control arrangement for altering the condition of such apparatus' when separation and reception, or collection, is not taking place as desired.

One form of apparatus with which the invention is adapted to be employed comprises the combination of a partially evacuated closed vessel and a magnetic field of such strength as to constrain uniform velocity ions projected within the vessel to motion on circles having radii which are a predetermined fixed function of the momentum of the ions. By such means it is known that ions having a common origin and traveling diiferent paths of equal curvature will, due to geometrical focusing action, substantially pass through a common region after 180 of travel.

In order for apparatus of the above type to have practical utility as a means for making isotopes available in quantity, it is necessary to collect separately the ions differing in mass i. e., the diiferent isotopes, so that they may be recovered to provide materials having greater proportions of certain isotopes than occur in nature. When, as is usual, the isotopes are collected in properly positioned receiver pockets, it is desirable to maintain the pockets in receiving condition only while satisfactory separation is taking place. This is especially true if the isotope of primary interest happens to comprise a very small fraction of those present. Accordingly it is an object of the invention to provide an arrangement for maintaining a collecting pocket in receiving condition only during the time satisfactory separation is taking place.

Another object of the invention is to provide a circuit arrangement responsive to the ratio between the isotopes being received for preventing the reception of at least one of the isotopes whenever such ratio departs a predetermined amount from the desired value.

Other objects and advantages of the invention will become evident from the following description when considered in connection with the accompanying drawing in which Fig. 1 shows a receiver control arrangement wherein the invention has been embodied; and Fig. 2 shows a modified embodiment of the invention.

The arrangements shown in the drawing have been made largely diagrammatic and consist of only those features necessary to a complete understanding of the invention; the various supporting structures and auxiliary equipment may take any suitable form known to those skilled in the art and constitute no part of the present invention. Accordingly such structure and equipment has not been shown since it would serve only to obscure rather than disclose the invention.

Referring to Fig. 1, there is shown a closed vessel 10 positioned in a strong magnetic field provided by a magnet one pole piece 11 of which is shown. The vessel 10 provides a space within which the electromagnetic separation of ions may take place and is preferably high y evacuated, although the presence of a small ice amount of gas is desirable under some circumstances to avoid so-called space charge effects.

Within the closed vessel 10 and also within the region of influence of the magnetic field produced by the pole piece 11 there is provided a source 12 of ions of a material the isotopes of which it is desired to separate and which, in conjunction with an accelerating electrode 13, serves to project in a direction normal to the magnetic field a stream or beam of high velocity ions. As is well known, these ions in traversing the magnetic field will be forced to follow circular orbits which results in the formation of the magnetic mass spectrum of the ions after approximately of travel from the accelerating electrode 13. If, as is here assumed, the ions consist primarily of two isotopes differing in mass, the ions of the greater mass will follow orbits having the curvature indicated by a path Q. Similarly ions of less mass will describe orbits of stronger curvature indicated by a path R. For convenience all ions passing through the region of focus of the path R will be referred to as the R beam and the receiver for this beam as the Rpocket. Also, the ions passing through the region of focus of the path Q will be referred to as the Q beam and its receiver as the Q pocket.

For collecting the ions thus segregated according to mass, a receiver housing 14 is positioned so that a slot 15 in its upper face substantially coincides with the foci of the Q and R beams. Within the housing 14 two electrically isolated pockets, R and Q, are mounted to receive the R and Q beams, respectively. The R pocket has a wall 16 for defining the R beam, which wall preferably is sloped sufiiciently to prevent its outer face being struck by any of tl1e Q beam. The Q pocket thus receives all of the ions passing through the slot 15 which are not intercepted by the R pocket. The deionizing currents to the Q and R pockets are electrically correct indications of the intensity of the Q and R beams, and in accordance with the invention, these two currents are connected through leads 17 and 18 to energize a ratiometer 19, the moving vane 20 of which controls the adjustment of a variable condenser 21 as indicated by the broken line 22 and for the purpose hereinafter described.

In apparatus of this type using a known feed material in the ion source 12 it is known that the ratio between the Q and R currents should approximate a certain value whenever satisfactory separation is taking place and that a sizeable departure from such value indicates unsatisfactory separation. This condition is utilized to prevent reception in at least one pocket whenever separation becomes unsatisfactory. To accomplish this a door 23 is biased by a spring 24 to the closed position shown in broken lines, wherein it prevents ions from entering the R pocket, and is movable to and held in the open position shown by a solenoid 25 as long as the solenoid 25 is suitably energized.

One suitable circuit arrangement for energizing the solenoid 25 only during the continuance of satisfactory separation is shown in Fig. 1 in which the solenoid 25 is adapted to be energized through contacts 26 from a suitable source of power 27 not shown whenever a time delay relay 28 is momentarily energized by closing a switch 29. The closing of the contacts 26 also completes a circuit through a time delay relay 30 in the output circuit of a vacuum tube 31 whose input is controlled by a resonant circuit the tuning of which is responsive to the ratiometer 19 as hereafter described. The relay 28 due to its time delay action maintains the contacts 26 closed an interval of time sufiicient for the relay 30 to become energized, if operating conditions are such that the tube 31 is conducting, in which case its contacts 32 will close to lock the solenoid 25 in energized con- -vent undesirable reception in the R pocket.

normal accelerating voltage.

unsatisfactory and the contacts 32 open, the switch 35 dition after the contacts 26 separate, and this condition will prevail as long as the tube 31 conducts.

The tube 31 is made responsive to the reading of the ratiometer 19 through the change in the variable condenser 21 which is connected as a capacitance detecting element in the grid circuit of a tube 33 comprising part of an oscillator which is here shown as being of the Hartley type. Variations in the capacitance of the condenser 21 against ground has the: eifect of changing the time constant of the resistance-capacitance filter 34 in series with the grid of the tube 33 and this, of course, determines the amplitude of the oscillations. An oscillator such as this is quite sensitive to variations in tuning and therefore a small departure of the reading of the ratiometer 19 from the desired value will decrease the amplitude of the oscillations sufticiently to render the tube 31 effectively non-conducting so that the relay 30 is de-energized, and its contacts 32 open to de-energize the solenoid 25, whereby the spring 24 closes the door 23 to pre- The relay 30 is preferably of the time delay type so that transitory changes in the reading of the ratiometer 19 such as might be caused by sparking will not function to close the receiver door 23.

Since the primary function of the arrangement of the invention is to prevent reception in the R pocket when separation is unsatisfactory the circuit arrangement above described may be employed to introduce a substantial change in the accelerating voltage applied between the ion source 12 and the accelerating electrode 13. One suitable circuit for this purpose is shown in Fig. 2 where in the solenoid 25, instead of actuating the door 23, is utilized to operate a switch 35. During normal operation the solenoid 25 is energized, as in Fig. 1, to hold the switch 35 against its upper set of contacts, thereby applying the voltage drop across a resistance 36 as the When separation becomes drops to the position shown which includes the voltage drop across a resistance 37 in the accelerating voltage. This higher accelerating voltage increases the radii of curvature of the ion beams Q and R so that they fall to the left of the receiver slot 15 as viewed in Fig. 1. Thus reception is prevented until the operator takes over and again adjusts, in a manner not shown, the apparatus for good separation.

It will be evident from the above description that the receiving condition of the apparatus is controlled by the ratio between the isotopes being separated in a manner such as to prevent reception when unsatisfactory separa tion occurs. Other similar arrangements can readily be devised without departing from the invention, the scope of which is pointed out in the appended claims.

We claim:

1. In apparatus for the electro-magnetic separation of 4 placing the apparatus in receiving condition, means responsive to the ratio between the isotopes being received, and electro-mechanical means controlled by said ratio responsive means for overriding said first named means and maintaining said apparatus in receiving condition.

2. In apparatus for separating isotopes, means for establishing a magnetic mass spectrum of the isotopes, receiver means for separately collecting the isotopes in at least two distinct spectral regions, means for measuring the ratio between the rates at which the isotopes are collected in said two regions, and means responsive to said last named means for rendering at least one of the receiver means non-collecting when said ratio departs from a predetermined value.

3. In an electro-tnagnetic type system for separating isotopes of a material, in combination, a receiver or collector for receiving separated isotopes of the material, control mechanism responsive to a condition indicative of a departure from desired normal reception of separated material for interrupting reception, and manual means for simultaneously causingreception to be originally initiated and rendering effective said control mechanism.

4. In an electro-magnetic type system for separating isotopes of a material, in combination, a receiver or collector for receiving separated isotopes of the material, control mechanism responsive to a condition indicative of a departure from desired normal reception of separated material for interrupting reception, and manual means for simultaneously causing reception to be originally initiated and rendering effective said control mechanism, said control mechanism including time delay means for preventing response of said mechanism to momentary conditions of departure from normal reception.

5. In an isotope separating apparatus of the electromagnetic type having an ion source, an ion accelerator and a collector for isotopic material, in combination, means for interrupting reception of isotopic material in the collector without otherwise suspending operation of the system, and means responsive to the ratio between two of the isotopes being received for rendering eifective the interrupting means.

6. Apparatus, as claimed in claim 5, wherein said interrupting means comprises a door physically movable to a position barring access of said beam to said collector.

7. Apparatus, as claimed in claim 5, wherein said in terrupting means comprises means for altering the accelerating potential existing between said source and said accelerator to physically move said beam away from said collector.

References Cited in the file of this patent UNITED STATES PATENTS 2,303,654 Newton Dec. 1, 1942 2,325,401 Hurlston July 27, 1943 2,341,551 Hoover Feb. 15, 1944 

